Cathode Ray Tube's (CRT's) are commonly used in many industrial and consumer electronic devices such as EKG-monitors, oscilloscopes, computer monitors, TV's, and the like. CRT based monitors typically include a CRT and control circuitry. The CRT generally comprises a glass tube with a “bottle neck” portion and a screen, an electron beam gun, and filter devices that are arranged to mask and guide the electron beam.
The screen is internally coated with a photo-emitting material (commonly, a phosphor-based chemical), which is activated by the electron beam. When electrons impinge on the inside of the screen, the energetic electrons collide with photo-emitting material that generate pixels on the display. Because the screen is not shaped as a perfect sphere and the displayed information is generally rectangularly shaped, an intensity of the electron beam is controlled by various circuits for different regions of the display.
Control circuitry includes horizontal, vertical, and east-west control circuits among other sub-circuits. While the horizontal control circuit manages an adjustment and a correction of horizontal deflection frequency, the vertical control circuit's main goal is to drive vertical deflection correction circuit. The east-west control circuit provides a correction signal for correcting geometric errors of the electron beam that result in an asymmetry between vertical and horizontal axes across a middle of the picture. This asymmetry may cause the displayed picture to have a pin-cushion or barrel shape with top and bottom corners of the picture not being vertically aligned with a middle of the picture. Another result of the east-west asymmetry may result in a circle in the picture appearing in an elliptical shape.
Thus, it is with respect to these considerations and others that the present invention has been made.